The present invention concerns a method for increasing seed yield in plants relative to control plants by increasing expression in a plant of a nucleic acid sequence encoding a Dwarf1 (DWF1) polypeptide.
Brassinosteroids (BRs) are a class of plant hormones that are important for promoting plant growth, division and development. The term BR collectively refers to more than forty naturally occurring poly-hydroxylated sterol derivatives, with structural similarity to animal (essentially cholesterol) and fungal (essentially ergosterol) steroid hormones. Among the plant BRs, brassinolide has been shown to be the most biologically active (for review, Clouse (2002) Brassinosteroids In The Arabidopsis Book: 1-23).
The BR biosynthetic pathway has been elucidated using biochemical and mutational analyses. BRs are synthesized via at least two branched biochemical pathways starting from the same initial precursor, cycloartenol (Klahre et al. (1998) Plant Cell 10: 1677-1690). The Arabidopsis Dwarf1 protein (DWF1; also called DIM for Diminuto, or CBB1 for Cabbage1) is involved in the conversion of an early precursor of BRs, 24-methylenecholesterol, to campesterol, as well as the conversion of isofucosterol to sitosterol, using flavin adenine dinucleotide (FAD) as a co-factor. This conversion proceeds in two sequential steps: an isomerization step (of the Δ24(28) bond into a Δ24(25) bond) and a subsequent reduction step of the new double bond.
Transgenic Arabidopsis plants that overexpress DWF1 did not display any clearly visible phenotype (Klahre et al. (1998), supra). Transgenic rice constitutively overexpressing the rice DWF1 orthologue have been produced, and typically display increased plant height, increased internode length, and increased number of spikelets per panicle (Hong et al., (2005) Plant Cell 17:2243-2254). Japanese patent application JP1999290082 describes a nucleic acid sequence encoding the rice DWF1 orthologue and its potential use to produce dwarfed plants upon reduced expression of the nucleic acid sequence.
Surprisingly, it has now been found that increasing expression in a plant of a nucleic acid sequence encoding a DWF1 polypeptide gives plants having increased seed yield relative to control plants.